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AJvYcCXLMUx5YO3wldB63Jm7bIr94t0tureLkkLyFSYC+Iq8TPf7wMnV/OMHpkubMUso/Isru1s3C2V3fA==@kvack.org X-Gm-Message-State: AOJu0Yzrpqb4T268ukG9/IFFa6sxeS9UTDYIuZgZqMORVqKqBsP1KMZr nw/zd5pmgCjj6Pv/pU95/T4fWzG7sMb8g+bk+Z+DPp9w/9rahD3SXcmUPGsJmJPHNGuratC/Rtz 2v6LrlgvUU+ufn4/y6109xOulBiY= X-Gm-Gg: ASbGncujxRlw+AAsio0XOk8szZi5TDaBf8RZbMtrTPq9PPIZG6iLKbV+M42JidRvr/w P6vvVkMcCs6d3mQiZkQA2m1xDIe7wx/8JsuyPgJCr9KMWeHWa1U/On9RFlMtEBYZ5QDRwxzexXU fIh4kLuhUMmL6bZkaETg== X-Google-Smtp-Source: AGHT+IE7BI6HNRvEYsbjvR7JB35pW97LgmJJTBXuV+FrmneMEc4oxMxZS6v6dB1H6kH/U6SDBGKlBQoEzbsb0fCA/SU= X-Received: by 2002:adf:fd84:0:b0:385:faf5:eb9f with SMTP id ffacd0b85a97d-38bf57c91e7mr30145364f8f.48.1737737188639; Fri, 24 Jan 2025 08:46:28 -0800 (PST) MIME-Version: 1.0 References: <20250124035655.78899-1-alexei.starovoitov@gmail.com> <2b2e6e04-b91d-4d9d-9cf9-5c690abe6746@suse.cz> In-Reply-To: <2b2e6e04-b91d-4d9d-9cf9-5c690abe6746@suse.cz> From: Alexei Starovoitov Date: Fri, 24 Jan 2025 08:46:17 -0800 X-Gm-Features: AWEUYZlJcdB9HixE4QFfndGOLwTnL9deAZ-R_-JU658ZMyXYSWK_edNK6hnlkKE Message-ID: Subject: Re: [PATCH bpf-next v6 0/6] bpf, mm: Introduce try_alloc_pages() To: Vlastimil Babka Cc: Matthew Wilcox , bpf , Andrii Nakryiko , Kumar Kartikeya Dwivedi , Andrew Morton , Peter Zijlstra , Sebastian Sewior , Steven Rostedt , Hou Tao , Johannes Weiner , Shakeel Butt , Michal Hocko , Thomas Gleixner , Jann Horn , Tejun Heo , linux-mm , Kernel Team , Marco Elver , Andrey Konovalov , Oscar Salvador Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspam-User: X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 7A4EA18000A X-Stat-Signature: qa5mr6fxhsk87nm7x3wo9bpbroca7xae X-HE-Tag: 1737737190-728873 X-HE-Meta: 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 S292w3AE zGiG+47h/9Yo3LvAeQd3PI4U1JeE6Tbjms6QQv1UWN/ZhB4LJavljPGRueIt89en+psXNVphwINhu6XzMH1q/Dn0+3jjhAuuK2i2qIqFZvI0Zc0v5UgY+MD0C9bMi8MFMXjKD4R34X4gQPZBxKci+qemHfYet4swOKElq5iCbqZ8g/5ALNlKmSBhMDOjIn/VAiqVV3SQOGQDwlOYUCugRBLinNPltx+iOpUH0+qw4/KOaoQy5uKSsSIFvcGkcD7sg2iVc6gbvNKncfyNmmE2Q/h1tmBLZUJlpqR+mohC+fQSmkXmE8nQc7ZZmk1oJ17lRrOIwrSuC1hYKPrUdnUluIJqP+BHVbxc2v2+6Gq1WKTlOLBPFkUkLJK2t476KgPowohYV33cbaUm2Avs= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, Jan 24, 2025 at 8:28=E2=80=AFAM Vlastimil Babka wr= ote: > > On 1/24/25 17:19, Alexei Starovoitov wrote: > > On Fri, Jan 24, 2025 at 6:19=E2=80=AFAM Vlastimil Babka wrote: > >> > >> On 1/24/25 15:16, Matthew Wilcox wrote: > >> > On Thu, Jan 23, 2025 at 07:56:49PM -0800, Alexei Starovoitov wrote: > >> >> - Considered using __GFP_COMP in try_alloc_pages to simplify > >> >> free_pages_nolock a bit, but then decided to make it work > >> >> for all types of pages, since free_pages_nolock() is used by > >> >> stackdepot and currently it's using non-compound order 2. > >> >> I felt it's best to leave it as-is and make free_pages_nolock() > >> >> support all pages. > >> > > >> > We're trying to eliminate non-use of __GFP_COMP. Because people don= 't > >> > use __GFP_COMP, there's a security check that we can't turn on. Wou= ld > >> > you reconsider this change you made? > >> > >> This means changing stackdepot to use __GFP_COMP. Which would be a goo= d > >> thing on its own. But if you consider if off-topic to your series, I c= an > >> look at it. > > > > Ohh. I wasn't aware of that. > > I can certainly add __GFP_COMP to try_alloc_pages() and > > Yeah IIRC I suggested that previously. Yes, as a way to simplify free_pages_nolock(). Hence I looked into it and added the above comment to the cover letter. Now I see that there are more and stronger reasons to use it. > > will check stackdepot too. > > Great, thanks. > > > I spotted this line: > > VM_BUG_ON_PAGE(compound && compound_order(page) !=3D order, page); > > that line alone was a good enough reason to use __GFP_COMP, > > but since it's debug only I could only guess where the future lies. > > > > Should it be something like: > > > > if (WARN_ON(compound && compound_order(page) !=3D order)) > > order =3D compound_order(page); > > > > since proceeding with the wrong order is certain to crash. > > ? > > That's the common question, should we be paranoid and add overhead to fas= t > paths in production. Here we do only for DEBUG_VM, which is meant for eas= ier > debugging during development of new code. > > I think it's not worth adding this overhead in normal configs, as the > (increasing) majority of order > 0 parameters should come here from > compound_order() anyway (i.e. put_folio()) As said we're trying to elimin= ate > the other cases so we don't need to cater for them more. Understood. I also agree with Matthew comment about page corruption. Whether compound_order(page) or order is correct is indeed a question. I'll wait for review on patch 3 before resubmitting with GFP_COMP included.